Disclosed herein are piezoelectric ink jet printheads and methods for making them.
Ink jet systems include one or more printheads having a plurality of jets from which drops of fluid are ejected towards a recording medium. The jets of a printhead receive ink from an ink supply chamber or manifold in the printhead which, in turn, receives ink from a source, such as an ink reservoir or an ink cartridge. Each jet includes a channel having one end in fluid communication with the ink supply manifold. The other end of the ink channel has an orifice or nozzle for ejecting drops of ink. The nozzles of the jets can be formed in an aperture or nozzle plate having openings corresponding to the nozzles of the jets. During operation, drop ejecting signals activate actuators in the jets to expel drops of fluid from the jet nozzles onto the recording medium. By selectively activating the actuators of the jets to eject drops as the recording medium and/or printhead assembly are moved relative to one another, the deposited drops can be precisely patterned to form particular text and graphic images on the recording medium.
Piezoelectric ink jet printheads typically include a flexible diaphragm and a piezoelectric transducer attached to the diaphragm. When a voltage is applied to the piezoelectric transducer, typically through electrical connection with an electrode electrically coupled to a voltage source, the piezoelectric transducer deflects or bends, causing the diaphragm to flex which expels a quantity of ink from a chamber through a nozzle. The flexing further draws ink into the chamber from a main ink reservoir through an opening to replace the expelled ink.
Piezoelectric transducers are bonded to the diaphragm with an adhesive. If exposed to oxygen, this adhesive can degrade over time and compromise the bond integrity between the piezoelectric transducer and the diaphragm, thus impeding or preventing drop ejection. Adhesives that are both robust to oxidation and suitable for this application are difficult to obtain.
Other proposed solutions have additional difficulties. For example, filling the piezoelectric transducer area with a liquid adhesive or epoxy and subsequently curing it would require multiple steps and additional time, and would also require mixing and dispensing the liquid adhesive or epoxy, which frequently introduces air bubbles into the adhesive that would need to be removed before curing. Another possible solution, creating a perimeter seal around the entire piezoelectric transducer area, would require additional capital machinery in the form of dispense robots and expertise.